Premoistened flushable wiper

ABSTRACT

A premoistened wiper having high initial wet strength in a wetting liquid, and lower wet strength when immersed in substantially neutral water to allow for flushability. The wiper includes a nonwoven web of fibrous material which is bonded together by a polymeric adhesive binder, with the bonded web being moistened until the time of use by a wetting liquid having an acid pH level which is safe for external use on the human body. The binder is composed of a material which is highly adhesive in an acid pH liquid to bind the fibers of the web together, and which is further resistant to weakening over the relatively long periods of shelf life of the wiper. However, the binder loses its binding strength in substantially neutral or alkaline flush water to allow for flushability. The bonded wiper is maintained with wetting liquid thereon within a moisture sealed container until the time of use, and readily loses strength and disintegrates when disposed of in the substantially neutral water of a sewer system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains generally to the field of toilet tissue andwipers, and more particularly to premoistened, non-woven wipers.

2. Description of the Prior Art

Wipers which are prepackaged in a moist environment are commonlyutilized by consumers for cleansing or wiping parts of the body,particularly where wash water is not readily available or cannot beconveniently used. Premoistened wipers are especially convenient fortravelers.

The premoistened wiper has found application as an anal cleansingtissue, complimentary to and occasionally a substitute for conventionaldry toilet paper. These wipers may also be utilized in applying orremoving make-up and in cleansing other parts of the body. Because ofsuch uses, the premoistened wipers are often disposed of by flushingthrough the toilet systems. Since the premoistened wiper must havesufficient wet strength to resist tearing and puncturing, these wipersdo not easily disintegrate in sewer systems and result in plugged drainsand sewer laterals.

Typically, the premoistened wipes have consisted of a non-woven web offibrous material, both natural and synthetic, with the fibers in the webbonded together by an adhesive material having good wet strengthqualities. The adhesive binder must also retain strength in the liquidused to wet the web, since this liquid often will contain bactericidesand other biological control agents as well as perfumes and emulsifiersto disperse these ingredients. The liquid medium on the web may also bemaintained at an acid pH level to further inhibit the growth oforganisms. Because the premoistened wiper must necessarily be able toretain its strength in the moist environment in which it is packaged,conventional techniques for achieving disintegration of fabrics in theflush water, such as utilizing ordinary water-soluble fiber binderadhesives, are not practical. Binder adhesives utilized in premoistenedwipers must also be capable of maintaining their adhesive strength in amoist environment for a shelf life storage period of from one month to ayear or more.

SUMMARY OF THE INVENTION

A premoistened wiper in accordance with this invention is capable ofproviding high wet strength until used, while disintegrating readily inflush water to allow for flushability and minimal obstruction ofsewerage systems. The premoistened wiper has a non-woven web substrateof fibers which are bonded together by a polymeric adhesive, with thebonded web being moistened by a liquid medium having an acid pH levelwhich is safe for external use on the human body. The fibers of the webremain strongly bound together when maintained in the acid pH liquidmedium, but are much more loosely bonded when the wiper has beenimmersed in substantially neutral toilet flush water, allowing the wiperto readily break up in the turbulent movement of the sewerage system.

The non-woven web is preferably formed of relatively short cellulosicfibers, preferably in the range of 1/16 inch to 1/2 inch, with longerfibers and synthetic fibers being added as desired to provide increasedstrength in those applications where it is needed. The short cellulosicfibers allow for a relatively soft feel desired in a toilet tissue,while further providing a substrate that is more susceptible tomechanical break-up and disintegration within the sewer system. Withsuch short fibers being utilized, the major strength of the web isprovided by the adhesive binder rather than the mechanical entanglementof the fibers of the web. The adhesive binder of the invention isdistributed uniformly over the non-woven web, and particularly it hasbeen found that the desired wet strength and flushability may beobtained utilizing binder materials of polymeric adhesives having theproperty of being weakly adhesive or soluble in a liquid medium ofneutral pH or higher, while being strongly adhesive and insoluble in aliquid medium of acid pH. The liquid medium in which the web ismaintained is at a low pH to provide the initial wet strength requiredby the user, while common flush water is of a high enough pH to causethe binder to weaken and allow disintegration of the web. The bindermaterials of the invention are further resistant to weakening in acid pHsolutions such that they may be maintained in moisture sealed packageswith the acid pH wetting liquid for relatively long periods of time, asrequired to obtain the necessary shelf life.

In accordance with the invention, such binder materials in the bondedwiper include acidic polymers, particularly polymeric polycarboxylicacids and polymeric functional derivatives thereof, and copolymers ofcertain water soluble monomers with water soluble monomers of carboxylicacids or functional derivatives of carboxylic acids. The adhesivebinders are further selected from those materials exhibiting a desirableresistance to weakening in acid pH, for the reasons indicated above.

The wetting liquid in which the bonded non-woven web is maintained isacidified by the presence therein of a mineral or organic acid in anamount sufficient to maintain the liquid medium at a desired pH level.The level of pH required in the liquid will vary depending on the typeof adhesive binder utilized and the pH level at which it insolubilizes.Generally, to minimize the possibility of skin irritation, the pH of thewetting liquid should be maintained at approximately 2.0 or higher.Other materials may be added to the wetting liquid for various purposes,such as perfumes and bactericides, and the wetting liquid may alsocontain a soluble surfactant which allows the perfumes and organicgrowth control agents to be dispersed in the liquid. These surfactantsmay also be selected to enhance the adhesive properties of the binder.

The binder is produced by forming a web of non-woven materials in adesired conventional fashion, saturating the web either before or afterthorough drying with a liquid solution of the binder material in asolvent to cause a pick-up by the web of a desired amount of the bindermaterial, drying of the web to remove the binder solvent, and thenimmersing the dried web in an acid pH solution which causes the bindermaterial to insolubilize and firmly bind together the fibers of the web.The insolubilizing of the binder adhesive may be accomplished byimmersing and maintaining the binder saturated web in the wettingliquid. Alternatively, the binder saturated web may be kept for shortperiods of time in a relatively low pH solution to thoroughlyinsolubilize the binder, and after removal of the bonded web from thedripping solution, the wetting liquid is applied to the bonded web andmaintained thereon until the time of use. The moistened wipers arepackaged in a moisture sealed container, in accordance with conventionalpackaging techniques, to prevent evaporation of the wetting liquid.

Further objects, features, and advantages will be apparent from thefollowing detailed description illustrating preferred embodiments of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A premoistened wiper in accordance with this invention has adequatelyhigh wet strength which is maintained over relatively long periods ofshelf life, and which is capable of disintegrating when immersed inneutral or basic normal tap water to allow for flushability. Generally,the wipers will be packaged and stacked in a water-tight package, withthe wetting liquid applied to the wipers comprising by weightapproximately 50 to 300% of the dry weight of the wiper itself. Thewiper must maintain its desired characteristics over the time periodsinvolved in warehousing, transportion, retail display, and storage bythe consumer. Required shelf lives are in the range of 2 to 6 months ata minimum, and the wipers are preferably capable of shelf lives as greatas 1 to 2 years.

The non-woven web itself is preferably formed of relatively shortfibers, such as wood pulp fibers, with the webs being formed by anycommon web manufacturing process. For example, the web may be producedby a conventional wet laying and wet creping process, or wet laying andthrough air drying, or by air laying the web, and by other techniquesutilized in the paper industry such as those used to produce towelingand tissue paper. Non-woven webs in accordance with this invention arepreferably formed to have relatively low wet cohesive strength when theyare not bound together by an adhesive. When such fibrous webs are bondedinternally by an adhesive which loses its bonding strength in tap waterand in sewer water, the webs will thus break up readily in the agitationprovided by flushing and moving through the sewer pipes.

The binder of this invention provides for the break-up of the wiperduring flushing because of its property of losing bonding strength bydissociation of association complexes between binder and fibers insubstantially neutral or basic tap water. Nonetheless, the binder hassubstantial adhesive strength to hold the web together during the periodof shelf life of the wiper and during its use. In accordance with thisinvention, the binder materials that provide this property are alkalisolubleacid insoluble polymers that provide lasting fiber to fiber bondsin an acid pH wetting liquid. As discussed below, such polymers includepolymeric polycarboxylic acids and polymers of functional derivativesthereof, and also polymers of various monomers, particularly vinylmonomers, with monomers of either carboxylic acids or functionalderivatives of carboxylic acids.

When polymers containing a large number of ether or ring oxygens, suchas cellulose, are mixed with other polymers containing many carboxylicgroups, strong association complexes are formed. The points ofattachment between the two different kinds of polymer chains arebelieved to be provided by hydrogen bonds. The association reaction thattakes place immediately in water base systems to form strong bonds, canbe regulated and reversed by changes in pH. This bonding is believed tobe analogous to the association reactions between certain polymersdescribed by K. L. Smith, A. E. Winslow, and D. E. Peterson,"Association Reactions for Poly (alkylene Oxides) and Polymeric Poly(carboxylic Acids)," Industrial and Engineering Chemistry, Vol. 51, p.1361 et seq, November, 1959. The binder molecules bridge between fibersand become attached by hydrogen bonding, thus providing a strong linkagebetween the fibers of the web. The bonds between the fibers are brokenwhen the bonded wiper is immersed in a liquid medium which has asufficiently high pH level to break the hydrogen bonds. However, loss offiber binding strength must be resisted by these binder materials at thelow pH levels at which they are maintained until the time of use. Theweakening of the bonded wiper in acid pH over a period of time isbelieved to occur in four ways: (1) depolymerization or cracking of thecellulose fiber molecules in acid solution, (2) scission of the bindermolecule polymer chains by hydrolysis to break the binder links betweenthe fibers, (3) leaching of the binder away from the fibers, byhydrolysis or oxidation, which solubilizes the binder, and (4) amaterial in the wetting liquid other than the binder competes forhydrogen bonding sites on the fibers and displaces the binder therefrom.The first cause of weakening of the bonded web is largely independent ofthe binder chosen since the breakdowns occur in the cellulose fibers.The other causes of weakening are more or less dependent on the bindermaterial.

Generally good adhesive properties which satisfy the requirements aboveare obtained with acidic polymers having equivalent weights between 100to 500 and molecular weights between approximately 20,000 and 1 million.Polymers of various carboxylic acids alone which meet these criteriawill provide the qualities required for an effective binder.Particularly good results are also obtained with binders formed ofcopolymers of water soluble or insoluble monomers with water solublemonomers which are either carboxylic acids or functional derivativesthereof. By way of illustration but not limitation, such copolymersinclude the following: styrene and maleic anhydride; methyl methacrylateand acrylic acid; ethyl acrylate and acrylic acid; vinyl acetate andcrotonic acid; acrylate esters and acrylic acid; methacrylate esters andacrylic acid; acrylate esters and methacrylic acid; and methacrylateesters and methacrylic acid. It has been found, however, that not allsuch carboxylic acid polymers and their derivatives have the necessaryresistance to weakening over reasonable shelf life periods. For example,commercially available sodium carboxy methylcellulose provides goodinitial wet strength when deposited on the fibers of a web andacidified, but rapidly weakens through hydrolysis, primarily by chainscission, when maintained in an acid medium, and this material losesmost of its binding strength within a month.

The binder material is prepared for application to a web by dissolvingin water using enough alkali to substantially neutralize all acidicgroups. The polymer solution, comprising a water solution of a salt ofthe acidic polymer, can then be applied to the web by various processes,including dipping the web in the polymer solution to cause completesaturation of the web with the solution, or spraying or rolling thesolution onto the web such that the polymer solution thoroughlysaturates through the web to contact the fibers therein and fill in thespaces in the web between the fibers. The saturated web is then dried tosubstantially remove the solvent water and allow the binder materialmolecules to settle into positions in which they can form linkagesbetween the fibers. After drying, the binder saturated web is thenimmersed in a liquid medium which has a low pH to cause associationreactions to take place between binder and fiber. The acid pH may beprovided in the solution by any suitable acid including hydrochloric,oxalic, fumaric, malic and phosphoric acid, or other mineral or organicacids which will not react with the binder material and which will notpresent safety problems when the wiper is used on the human body.Similarly, the wetting liquid in which the bonded web is maintaineduntil the time of use will include an acid, such as those listed above,to control the pH of the wetting liquid at a level at which the bondingin the adhesive binder remains strong. Other ingredients will also bepresent in the wetting liquid, such as perfumes, bactericides, ethylalcohol, and emulsifiers and surfactants to allow dispersion of theother ingredients within the wetting liquid.

It is found that the surfactants utilized in the wetting liquid can havea substantial effect on the quality of the binding of the web. Forexample, nonionic emulsifiers in the wetting liquid tend to weaken thebinder. It is theorized that the emulsifiers compete for hydrogenbonding sites with the molecules of the binder and thus weaken thequality of the bonds. Conversely, the use of anionic surfactants,particularly those having a carboxylic base, do not substantially weakenthe binder, and actually increase the wet strength above the level foundwithout the use of such surfactants. For example, the bonding may bestrengthened by the use of sulfonic dispersants (e.g. polymerized sodiumsalts of alkyl naphthalene sulfonic acid) and carboxy dispersants(sodium salts of polycarboxylic acid and polyacrylic acid). Thesedispersants also do not substantially affect the loss of strength thatoccurs when the wiper is immersed in neutral water solution, and do notsubstantially inhibit the solubility of the binder itself.

The following examples are provided as illustrative of the invention,but are not to be construed as being exhaustive or as limiting theinvention to the specific details thereof.

EXAMPLES 1-4

In the examples that follow, the measurement of wet and dry tensilestrength was determined according to the following method. Six inch bysix inch sheets of the selected non-woven web were heated in an oven at105° C. for 15 minutes. The dry sheets were then stored in a desiccatorloaded with Drierite calcium sulfate. Two dry 6 × 6 inch sheets wereweighed separately, and were then saturated in the binder solution undertest and passed through rubber ringer rolls to remove excess liquid. Thesheets were placed side-by-side between two pieces of 20 mesh Teflonscreen and dried in a photographic print dryer set at 105° C. for 5minutes, and were then cooled in a desiccator. The resultingsubstantially dry sheets contained less than 10% water on the dry weightof the web. Overdrying of the webs to moisture levels below 1 or 2% atelevated temperatures is avoided because heating for prolonged periodsof time will crosslink the binder material. The dried sheets wereweighed, and four 1 × 4 inch strips from each sheet were cut. Where theweb was a creped web, the sheets were cut such that the creping wrinklesran with the long 4 inch dimension of the strip to allow measurement ofthe tensile strength of the web in the cross machine direction (CD) ofthe web. The dry weight binder content of the web, in grams of binderper 100 grams of dry weight web, was calculated by subtracting theinitial dry weight of the web from the weight of the web after applyingthe binder and drying, dividing that quantity by the initial weight ofthe web and multiplying by 100 grams. 100 ml. of 500 mg./literphosphoric acid solution was placed in a clean square petri dish. Theeight strips of paper were immersed in the acid liquid and allowed tosoak at room temperature for eighteen hours. The pH of the soakingliquid was measured at the beginning and end of the soaking time. Aftersoaking, the strips were blotted between two paper towels and thetensile strength of four wet, acid soaked strips were measured. Theother four strips were placed in two liters of tap water contained in a4 liter beaker. An electric mixer equipped with a 2 inch marine impellerwas positioned near the center of the four liter beaker such that thebottom of the impeller was 1 inch from the surface of the water. Theimpeller was turned on at a speed of 100 rpm for one hour. The stripswere then removed, blotted between paper towels and the wet tensilestrengths measured.

To determine relative break-up times between different treated wipers,the following testing procedure was utilized. A Tergotometer (Model7243, United States Testing Co., Inc., 1415 Park Avenue, Hobokken, N.J.)was modified such that each two liter stainless steel beaker in theTergotometer will allow overflow of water into the temperature controlchamber. Nineteen 3/16 inch diameter holes were drilled in each tub,spaced equally in a ring around the wall of the tub, at a distance fourinches from the bottom of the tubs. Each tub was equipped with aseparate cold water supply line and a flow meter capable of measuringflows of 500 to 1,000 ml./min. 3 × 3 inch squares of the wiper to betested were cut, and all three squares were put in one 2-liter stainlesssteel tub in the Tergotometer. The tub was filled with cold tap waterand the agitator started running at 100 cycles per minute. Cold tapwater was run into the mixing system at a flow rate of 800 millimetersper minute. Liquid is allowed to overflow through the perforations inthe tub. The time was measured from the start of mixing, and mixing wascontinued until all three squares of wiper were broken down to piecessmaller than 3/4 inch in diameter. The elapsed time required to obtainthe specified degree of break-up was recorded for each test.

The following binder solutions were prepared:

Two percent acrylic acid-acrylic ester copolymer solution was preparedby mixing 46 grams of 40% solids Acrysol ASE-75 Latex obtained from theRohm & Haas Co., with 926 grams of distilled water. Twenty-eight gramsof 10% sodium hydroxide was added thereto to neutralize the solution.

Two percent acrylic acid-acrylic ester copolymer solution was preparedby mixing 70 grams of 25% solids XD-30070 Latex from Dow ChemicalCompany, with 900 grams of distilled water. Thirty grams of 10% sodiumhydroxide was added thereto to neutralize the solution.

Two percent styrene-maleic anhydride copolymer solution was prepared bydissolving 20 grams of Scriptset 500 powder obtained from the MonsantoCompany, in 980 grams of distilled water. The mixture was heated andstirred as necessary to result in complete solution of the powder.

A two percent vinyl acetate-crotonic acid copolymer solution wasprepared from a concentrate formed by stirring 120 grams of VinacASB-516 obtained from Air Products & Chemicals Company, and 1,025 gramsof distilled water containing 55 grams of 10% sodium hydroxide. Twohundred grams of the concentrate was mixed with 800 grams of water andwas heated and stirred to completely dissolve the polymer. A fivepercent vinyl acetate-crotonic acid copolymer was also prepared forsubsequent procedures by mixing 500 grams of the concentrate with 500grams of water, and was heated and stirred to completely dissolve thepolymer.

A standard, non-woven substrate web for evaluating the binders was madeby refining a mixture of 75% bleached softwood kraft (SWK) pulp and 25%bleached hardwood kraft (HWK) pulp fibers to a Canadian standardfreeness of 550 ml. The refined pulp was processed on a commercial papermachine to make wet creped paper with a basis weight of 40 lbs./3,000sq. ft.

The procedures specified above for determining wet tensile strength andbreak-up time were utilized for each of the 2 percent concentrationbinder solutions to obtain the data set forth in Table I below. Theamount of binder pickup by the web in terms of the dry weight of thebinder material to the dry weight of the web is also given in Table I.

                                      TABLE I                                     __________________________________________________________________________                          CD                                                                            Wet Tensile                                                              Binder in                                                                          g./cm.  Breakup                                                          Web  Dilute                                                                            Tap Time,                                           Binder   Polymer Type                                                                          g./100 g.                                                                          Acid                                                                              Water                                                                             Min.                                            __________________________________________________________________________    2% Acrysol                                                                             Acrylic acid-                                                                         2.5  340 160 30                                                 ASE-75                                                                              acrylic ester                                                                 copolymer                                                            2% Dow   Acrylic acid-                                                                         3.1  395  98 18                                                 XD-30070                                                                            acrylic ester                                                                 copolymer                                                            2% Script-                                                                             Styrene-maleic                                                                        3.6  190 114 25                                                 set 500                                                                             anhydride                                                                     copolymer                                                            2% Vinac Vinyl acetate-                                                                        2.2  123  87  4                                                 ASB-516                                                                             crotonic acid                                                                 copolymer                                                            __________________________________________________________________________

EXAMPLES 5-8

Fibers composed of 75% bleached Canadian softwood kraft pulp and 25% 1.5denier rayon fibers, cut to 1/4 inch length, were slurried in water andmade into a paper web having a basis weight of 30 lbs./3,000 sq. ft. onhandsheet equipment. The dried sheets were dipped in the four twopercent binder solutions specified above in Examples 1-4 and dried, andthe procedures outlined in Examples 1-4 were followed to determine wettensile strength and breakup time. The results of these tests are givenbelow in Table II.

                                      TABLE II                                    __________________________________________________________________________                          CD                                                                            Wet Tensile                                                              Binder in                                                                          g./cm.  Breakup                                                          Web  Dilute                                                                            Tap Time,                                           Binder   Polymer Type                                                                          g./100 g.                                                                          Acid                                                                              Water                                                                             Min.                                            __________________________________________________________________________    2% Acrysol                                                                             Acrylic acid-                                                                         2.3  126 67  6                                                  ASE-75                                                                              acrylic ester                                                                 copolymer                                                            2% Dow   Acrylic acid-                                                                         5.2  102 29  5                                               XD-30070                                                                         acrylic ester                                                                       copolymer                                                            2% Scrip-                                                                              Styrene-maleic                                                                        3.4   88 55  2                                                  set 500                                                                             anhydride                                                                     copolymer                                                            2% Vinac Vinyl acetate-                                                                        2.3   87 56  3                                                  ASB-516                                                                             crotonic acid                                                                 copolymer                                                            __________________________________________________________________________

EXAMPLES 9-22

Forty lbs./3,000 sq. ft. wet creped paper, made from 75% softwood kraftand 25% hardwood kraft pulp, was dipped in and saturated with 2% sodiumAcrysol ASE-75 (acrylic acid-acrylic ester copolymer) water solution anddried. Samples of this paper were separately soaked in acidifyingsolutions containing four different acids at various levels ofconcentration, as indicated below.

Four acid stock solutions were prepared to yield acid reagentconcentrations of 0.01 grams/ml. of water, as follows:

    ______________________________________                                                               Acid     Distilled Water                                                      Amount,  Amount,                                       Acid       Type        g.       g.                                            ______________________________________                                        Hydrochloric                                                                             Strong Mineral                                                                            27       973                                            37% HCl                                                                      Phosphoric Weak Mineral                                                                              11.8     988                                            85% H.sub.3 PO.sub.4                                                         Oxalic     Strong Organic                                                                            14       986                                            Oxalic                                                                        Acid.2H.sub.2 O                                                              Malic      Weak Organic                                                                              10       990                                            100%                                                                          Malic Acid                                                                   ______________________________________                                    

The tensile strengths of the bonded web samples after soaking in theacid solutions for 18 hours, were measured in accordance with testprocedures specified in the foregoing Examples. Acid pH values wererecorded in the soaking solutions before and after the bonded web wassoaked. The tensile strength of the web after soaking is given below inTable III. The wet tensile strength for a web sample soaked in wateralone is also given in Table III for comparison purposes.

                                      TABLE III                                   __________________________________________________________________________    Stock                                                                         Diluted to                                                                    1 liter   Concen-                                                                            Solution pH                                                                              CD Wet                                                  (ml. of                                                                             tration  AFter Soaking                                                                        Tensile                                             Acid                                                                              stock)                                                                              mg./liter                                                                          Initial                                                                           Web    g./cm                                               __________________________________________________________________________    None                                                                              --    --   6.7 7.4     64                                                 HCl  5     50  2.8 3.3    170                                                 "   10    100  2.5 2.8    238                                                 "   15    150  2.3 2.6    308                                                 "   20    200  2.2 2.4    333                                                 H.sub.3 PO.sub.4                                                                  10    100  2.9 3.6    205                                                 "   20    200  2.7 3.0    248                                                 "   40    400  2.4 2.7    310                                                 "   60    600  2.3 2.5    345                                                 Oxalic                                                                            10    100  2.8 3.3    205                                                 "   20    200  2.5 2.8    266                                                 "   50    500  2.2 2.4    370                                                 Malic                                                                             20    200  3.1 3.7    217                                                 "   40    400  3.0 3.3    278                                                 "   80    800  2.8 3,0    315                                                 __________________________________________________________________________

EXAMPLES 23-46

A 2% Acrysol ASE-75 solution and 2% and 5% Vinac ASB-516 solutions wereprepared as outlined in Examples 1-4 for use as binders for a variety ofnon-woven web substrates. Conventional wet laid, paper was prepared fromthe following fibers:

(1) Bleached Canadian softwood kraft (SWK) pulp.

(2) Bleached Canadian hardwood kraft (HWK) pulp.

(3) 1.5 denier rayon chopped to 1/4 inch length.

(4) A blend of 75% SWK and 25% chopped 1/4 inch length rayon.

(5) A blend of 75% SWK and 25% 3.0 denier Kuralon No. 4,polyvinylalcohol fibers, chopped to 1/4 inch length.

(6) Cotton linters.

(7) A blend of 75% SWK and 25% cotton linters.

(8) 1.5 denier polyester fibers chopped to 9/16 inch length.

The test procedures specified above in Examples 1-4 were used tosaturate all of the webs with the various binders and to acidify thewebs in phosphoric acid solution to insolubilize the binder. Theprocedures of Examples 1-4 were also utilized to determine wet tensilestrength after soaking in acid and after soaking in substantiallyneutral tap water, and to determine the breakup time after soaking inthe tap water. This data is given in Table IV below.

                  TABLE IV                                                        ______________________________________                                                          CD Wet                                                                        Tensile, g/cm                                                                          Breakup                                                         Fiber      Dil.   Tap   Time,                                    Substrate    Binder     Acid   Water Min.                                     ______________________________________                                        Bl. SW kraft 2% Acrysol 200    82    8                                        paper        2% Vinac   98     54    2                                                     5% Vinac   165    75    9                                        Bl. HW kraft 2% Acrysol 92     36    8                                        paper        2% Vinac   65     26    2                                                     5% Vinac   100    48    6                                        1/4-inch rayon                                                                             2% Acrysol 46     22    0.5                                                   2% Vinac   28      9    1                                                     5% Vinac   42     40    2                                        75% SW kraft and                                                                           2% Acrysol 137    76    7                                        25% Rayon    2% Vinac   98     53    2                                                     5% Vinac   170    92    7                                        75% SW kraft and                                                                           2% Acrysol 170    68    10                                       25% Kuralon  2% Vinac   91     36    2                                                     5% Vinac   160    80    8                                        Cotton linters                                                                             2% Acrysol 16     14    10                                                    2% Vinac   31     17    10                                                    5% Vinac   67     35    10                                       75% SW kraft and                                                                           2% Acrysol 39     27    3                                        25% cotton   2% Vinac   33     14    1                                                     5% Vinac   68     35    4                                        9/16-inch    2% Acrysol 121    93    1                                        polyester    2% Vinac   390    210   6                                                     5% Vinac   1150   830   12                                       ______________________________________                                    

Generally, premoistened wipers in practical application must be strongenough so that they will not tear when pulled from dispensingcontainers, or puncture when used for wiping. It has been found that wetwipers with tensile strengths of 140 g./cm. or higher satisfactorilymeet this requirement. To obtain desirable breakup of the wipers intoilet flush water, it is preferred that the tensile strength of thewiper immersed in neutral water should drop below approximately 70g./cm. It may be noted, however, that lower wet strengths aresatisfactory where the dispensing of the wipers from their packagingdoes not require vigorous pulling and strain on the wipers. Furthermore,the decrease in tensile strength and breakup time after neutral watersoak which is associated with all of the binders of this invention is ofsubstantial utility in preventing clogged drains and sewer systems, evenwhere the strengths of the wiper in neutral flush water are not as lowas are obtained with standard dry tissue paper.

EXAMPLES 47-50

A 40 lb./3,000 sq. ft. web of wet creped paper made from 75% softwoodkraft and 25% hardwood kraft fibers was saturated with bonding solutionsat four concentration levels. Four Acrysol ASE-75 (acrylic acid-acrylicester copolymer) solutions were prepared at concentration levels of 1%,2%, 3%, and 4% as indicated below:

    ______________________________________                                                        1%    2%     3%      4%                                       ______________________________________                                        Water, grams      963     926    889   852                                    40% Acrysol ASE-75 Latex, g.                                                                    23      46     69    92                                     10% NaOH, g.      14      28     42    56                                     ______________________________________                                    

The wet strength of the wiper after acid soak, and the wet strength andbreakup time after water soak were determined according to theprocedures specified in Examples 1-4 above. The resulting data are givenin Table V below. Test results for a web having no binder are also givenin Table V for comparison purposes.

                  TABLE V                                                         ______________________________________                                                            CD Wet Tensile,                                           Na Acrysol          grams/cm.                                                 ASE-75  Acrysol Pickup,                                                                           Dilute  Tap    Breakup Time,                              in Dip, %                                                                             g./100 g. fiber                                                                           Acid    Water  minutes                                    ______________________________________                                        None    --           55     --      1                                         1       1.1         220     107    13                                         2       3.1         328     144    38                                         3       5.2         278     185    45                                         4       7.9         257     154    54                                         ______________________________________                                    

EXAMPLES 51-54

A web substrate formed of Canadian softwood kraft pulp was soaked in awater solution of 75% neutralized Sodium Acrysol ASE-75 binder, with aresulting pickup of 2.7 grams of binder per 100 grams of dry web. Thebonded web was immersed in water solutions of four acids, phosphoric,hydrochloric, oxalic, and malic. The cross machine dimension (CD) wettensile strength of the bonded webs was measured after initial 18 hoursoaking in the acid solutions and again after six months of soaking inthe acid solutions. These data are given below in Table VI, which alsogives the pH of the acid solution at the beginning and at the end of thesix month period.

                  TABLE VI                                                        ______________________________________                                        Binder                                                                               Pickup                    CD Wet Tensile,                                     g./           pH          grams/cm.                                    Type     100 g.  Acid    Start                                                                              6 Months                                                                             Start                                                                              6 Months                            ______________________________________                                        Acrysol  2.7     H.sub.3 PO.sub.4                                                                      2.50 2.55   329  215                                 ASE-75   HCl     2.60    2.60 244    179                                      (75% Neut.)                                                                            Oxalic  2.51    5.10 289    217                                                       Malic   2.51 2.71   461  419                                 ______________________________________                                    

It is apparent that the bonded web loses some tensile strength over theaging period, with this weakening being due to the mechanisms discussedabove, including breakdown of the cellulosic fibers in the web. Thesebinders are, however, substantially resistant to weakening such as bychain scission, since the tensile strengths of the aged bonded webs arefar greater than the tensile strength of an unbonded web, which isgenerally about 50 to 60 g./cm. or less.

EXAMPLES 55-57

A mixture of 75 parts bleached softwood kraft pulp and 25 parts bleachedhardwood kraft pulp was refined to a Canadian standard freeness of 550ml., and was processed on a commercial paper machine to make a wetcreped paper with a basis weight of 40 lbs./3,000 sq. ft. The dry paperwas saturated with a solution of 2% sodium Acrysol solution (sodiumacrylic acid-acrylic ester copolymer) made by mixing 46 grams of 40%solids Acrysol ASE-75 obtained from the Rohm & Haas Co., with 926 gramsof distilled water. The Acrysol was neutralized by adding 28 grams of10% sodium hydroxide. The dried saturated web contained 2.4 grams sodiumAcrysol per 100 grams of the web itself. A first wetting liquid wasprepared comprising 993 grams of distilled water, 4 grams of 85%phosphoric acid, and 3 grams of Daxad 11 from W. R. Grace Co., asulfonic dispersant (polymerized sodium salts of alkyl napthalenesulfonic acid). A second wetting liquid was prepared comprising 986grams of distilled water, 4 grams of 85% phosphoric acid, and 10 gramsof Tamol 850 from the Rohm & Haas Co., a carboxy dispersant. A thirdwetting liquid was prepared comprising 991 grams distilled water, 4grams 85% phosphoric acid, and 4.6 grams Goodrite K743 from B. F.Goodrich Co., a poly-acrylic acid. Sheet of the binder saturated driedpaper were moistened with the three wetting liquids, squeezed to removeexcess liquid, and stored wet for 24 hours. Cross machine direction (CD)tensile strength measurements before and after soaking in tap water weredetermined as indicated in Examples 1-4 above. These data are given inTable VII, along with similar data for a bonded sheet stored in an acidwetting liquid which contained no dispersant.

                  TABLE VII                                                       ______________________________________                                                     uz,14/25 CD Wet Tensile, g./cm.                                                             Breakup                                                     pH of              After 1-Hour                                                                           Time                                     Surfactant                                                                             Acid Soak Initial  Water Soak                                                                             Minutes                                  ______________________________________                                        None     2.4       449      248      30                                       Sulfonic                                                                      Dispersant                                                                    (Daxad 11)                                                                             2.0       489      237      40                                       Carboxy                                                                       Dispersant                                                                    (Tamol 850)                                                                            2.8       457. 176 34                                                Polyacrylic                                                                   acid     1.9       511      193      44                                       (Goodrite                                                                     K743)                                                                         ______________________________________                                    

These dispersants thus allow incorporation of the desired non-watersoluble ingredients into the wetting liquid, while maintaining orenhancing the wet strength of the bonded web, and do not substantiallyaffect the loss of strength of the bonded web when immersed in neutralwater. Ethyl alcohol may also be added to the wetting liquid to aid inemulsification of the perfumes and organic stabilizers.

The wetting liquid is maintained on the bonded wiper and evaporationprevented by sealing the wetted wipers in a moisture proof container.The acidity of the wetting liquid aids in maintaining the organicstability of the packaged wipers, since low pH inhibits the growth ofsome organisms, particularly where the pH is maintained below about 4.0or 5.0. Since very low pH levels can result in irritation of human skin,it is preferred that the pH of the wetting liquid be greater thanapproximately 2.0. This level of acidity is not unusual in consumerproducts. For example, most soft drinks have a pH level between about2.0 and 4.0.

It is understood that the invention is not confined to the particularembodiments described herein as illustrative of the invention, butembraces all such modifications thereof as may come within the scope ofthe following claims.

We claim:
 1. A premoistened wiper having high initial wet strength andlower wet strength when immersed in a substantially neutral or alkalineliquid to allow for flushability, comprising:(a) a non-woven web offibrous materials; (b) an adhesive binder distributed through said webbonding together the fibrous material of said web, said binderconsisting esentially of an acid insoluble-alkali soluble acidic polymerwhich is resistant in acid liquid to weakening of the bonding betweenthe fibers of said web; (c) a wetting liquid in contact with said bondedweb having an acid pH which is safe for external use on the human body;and (d) alkali metal ions distributed through said web and available forassociation with said acidic polymer.
 2. The wiper of claim 1 whereinsaid acidic polymer is an acid insoluble-alkali soluble polymericpolycarboxylic acid which is resistant in acid liquid to weakening ofthe bonding between the fibers of said web.
 3. The wiper of claim 1wherein said acidic polymer is an acid insoluble-alkali solublepolymeric functional derivative of a polycarboxylic acid which isresistant in acid liquid to weakening of the bonding between the fibersof said web.
 4. The wiper of claim 1 wherein said acidic polymer is anacid insoluble-alkali soluble polymer of a monomer material with acarboxylic acid and which is resistant in acid liquid to weakening ofthe bonding between the fibers of said web.
 5. The wiper of claim 1wherein said acidic polymer is an acid insoluble-alkali soluble polymerof a monomer material with a functional derivative of a carboxylic acidand which is resistant in acid liquid to weakening of the bondingbetween the fibers of said web.
 6. The wiper of claim 1 wherein saidacidic polymer is selected from the group consisting of a copolymer ofstyrene and maleic anhydride, a copolymer of acrylate esters andmethacrylic acid, a copolymer of methyl methacrylate and acrylic acid, acopolymer of acrylate esters and acrylic acid, a copolymer ofmethacrylate esters and acrylic acid, a copolymer of ethyl acrylate andacrylic acid, a copolymer of vinyl acetate and crotonic acid, and acopolymer of methacrylate esters and methacrylic acid.
 7. The wiper ofclaim 1 wherein the fibrous material of said non-woven web is selectedfrom the group consisting of fibers of wood pulp, rayon, cotton,polyvinylalcohol, polyester, and mixtures thereof.
 8. The wiper of claim1 wherein said wetting liquid consists essentially of a solution ofwater and an acidifying agent selected from the group consisting ofphosphoric acid, malic acid, fumaric acid, oxalic acid, and hydrochloricacid, said acidifying agent being present in said wetting liquid in anamount sufficient to maintain said wetting liquid on said bonded web ata pH of no greater than 5.0.
 9. The wiper of claim 1 wherein saidwetting liquid includes therein a surfactant selected from the groupconsisting of sulfonic surfactants and carboxy surfactants.
 10. Thewiper of claim 1 wherein said wetting liquid includes a surfactantselected from the group consisting of polymerized sodium salts of alkylnaphthalene sulfonic acid, sodium salts of carboxylic acids, andpolyacrylic acid.